Investigation of Switching Oscillations for Silicon Carbide MOSFETs in Three-Level Active Neutral-Point-Clamped Inverters

Abstract

This article investigates the multifrequency switching oscillations of silicon carbide (SiC) MOSFETs in three-level active neutral-point-clamped (3L-ANPC) inverters under three typical commutation modes (i.e., the full mode, outer mode, and inner mode). Multiple switching-oscillation components with various frequencies are identified theoretically for both the full- and outer-mode commutations, due to their switching-loop diversities. Oppositely, the inner mode exhibits a single oscillation component as only one switching loop is involved. Three types of double-pulse tests (DPTs) are conducted on a 3L-ANPC inverter demonstrator with SiC MOSFETs, and the switching-oscillation components are extracted accordingly, which match well with the theoretical derivations. Moreover, other switching characteristics closely related, i.e., the oscillation peaks, current overshoots, capacitive charges, and switching energies, are studied and benchmarked according to the DPT results. It is concluded that the full- and outer-mode commutations share similarities in terms of switching oscillations, current overshoots, capacitive charges, and turn-on energies. The theoretical findings from this work provide a comprehensive knowledge of the multifrequency oscillation mechanisms associated with fast-switched 3L-ANPC inverters. Accordingly, the critical parasitic components are identified, and specific design considerations are proposed to achieve switching-performance improvements.